1. Field of the Invention
The present invention relates to a developer transport unit, an image forming apparatus, a method of transporting developer, a program for implementing a method of transporting developer, and a storage medium storing a program, and more particularly to, a developer transport unit, an image forming apparatus, a method of transporting developer, a program for implementing a method of transporting developer, and a storage medium storing a program to supply developer to a development unit from a developer storage vessel via an sub-storage vessel while managing developer supply appropriately by detecting developer amount in the developer storage vessel correctly.
2. Description of the Background Art
Image forming apparatuses using electrophotography conduct image forming operations as follows. An electrostatic latent image formed on a photoconductor is developed as a toner image by a development unit using toner (used as developer), and then the toner image is transferred from the photoconductor to a recording sheet. Such image forming apparatuses may be equipped with a toner supply mechanism, and such toner supply mechanism may use a sub-tank to transport toner from a toner bottle to the development unit. Specifically, toner in the toner bottle is ejected to the sub-tank by a toner pump to store toner in the sub-tank. Then, toner stored in the sub-tank is transported to the development unit by rotating a toner transporting coil when the development unit requires a certain amount of toner, as disclosed, for example, in JP-2007-163793-A.
Further, in such conventional toner supply mechanism, in general a spiral pattern is formed in an internal face of the toner bottle from a bottom side to a toner ejection port of the toner bottle. When the toner bottle rotates, the spiral pattern in the toner bottle moves toner to the toner ejection port, where the toner is transported to the sub-tank by the toner pump.
For optimum imaging, a certain amount of toner is required to be constantly stored in the sub-tank of the toner supply mechanism. To check an amount of toner (toner amount) in the sub-tank, a toner amount sensor such as an electromagnetic sensor is disposed in the sub-tank. In conventional toner supply mechanisms, when the toner amount sensor detects that the toner amount in the sub-tank decreases to a certain amount or less, the toner bottle is rotated and the toner pump is driven simultaneously, moving toner in the toner bottle to a toner ejection port where the toner is transported to the sub-tank by using the toner pump until the toner amount in the sub-tank becomes a certain amount.
However, such conventional technology may have some drawbacks for appropriately managing amount of toner remaining in a toner bottle, and a toner pump for transporting toner from a toner bottle to a sub-tank.
A toner pump takes a certain amount of time (supply time) to supply toner from the toner bottle to the sub-tank, determined by the amount of time needed for the toner in the sub-tank to reach a certain amount, and such supply time may change or vary depending on the amount of toner already in the toner bottle at any given time. For example, when the toner amount in the toner bottle decreases, the toner supply time becomes longer compared to when the toner amount in the toner bottle is in a toner-full condition.
However, in conventional technologies, no consideration may not be given to the fact that the toner amount eject-able from the toner bottle to the sub-tank decreases as the toner amount in the toner bottle decreases. Rather, in conventional technologies, it is assumed that the toner amount in the toner bottle remains constant, and that the toner amount ejected from the toner bottle to the sub-tank is calculated based on a rotation time of the toner bottle. Accordingly, when toner amount in a toner bottle becomes little and toner may not exist near the toner ejection port, the toner bottle needs to be is rotated for a given rotation time so that toner is moved to nearby of toner ejection port in the toner bottle. Although toner may not be ejected from a toner bottle actually during such rotation, in a conventional calculation process for calculating remaining amount of toner, it is assumed that toner is ejected from a toner bottle. As a result, toner remaining amount obtained by conventional calculation and toner remaining amount actually remaining in the toner bottle may have a difference, by which toner empty condition (or no toner condition) cannot be alarmed at a correct timing.
Further, in conventional technologies, when toner amount in a toner bottle decreases, toner may exist at a location far from a toner ejection port of toner bottle but toner may not exist so much at a location nearby of toner ejection port depending on a shape of toner bottle. Even in such condition, in conventional technologies, a toner pump may be rotated simultaneously with a rotation of toner bottle. As a result, the toner pump may suck mostly air in the toner bottle, and air leak may occur due to a characteristic of the toner pump, and a stator in the toner pump may not function properly and the toner pump may malfunction.